A strong body of evidence has emerged over the recent years suggesting a relationship between obstructive sleep apnea (OSA) and depressive symptoms. The frequent co-occurrence of the two conditions makes it necessary that their co-morbidity and the pathogenetic relations between them should be studied in detail. Most of the studies to date have found a significant correlation between depressive symptoms and OSA. The basic pathogenetic mechanisms involved are disturbed neurotransmission, synaptic remodeling and neuronal death (neuroplasticity). Further longitudinal studies are needed to completely elucidate the OSA-depression relationship. Better knowledge of the problem may significantly improve diagnostics and therapeutical options in that group of patients.